1. Field of the Invention
This invention pertains to a valve for use with a venting tube coupled to a gasoline storage tank for providing air intake for pressure equalization as gasoline is removed from the tank, while at the same time providing valve structure which can seal itself during tank refill operations against venting of gas fumes to the atmosphere.
2. Prior Art
Antipollution requirements have attempted to restrict the venting of gasoline fumes into the atmosphere for many years. For gas stations, these requirements necessitate the cooperation of tanker operators who refill gasoline storage tanks. Despite the importance of conversation and clean air regulations, refill operations continue to result in substantial air pollution through release of gas fumes accumulated in gas storage tanks.
A basic tank storage system is illustrated in FIG. 1. Typically, the tank 10 is below ground level 11. The gas pump 12 is coupled to the stored gas 13 within the tank via conduit 14. When the tank is full of liquid gas, there is little remaining volume left for gas vapor. As gas is removed through the pump 12, the unfilled volume 15 increases. To prevent collapse of the tank due to vacuum forces arising with fluid discharge, a venting tube 16 is coupled to the open space 15 at the top of the tank. This venting tube enables pressure equalization between the contained volume within the tank and outer atmosphere.
Such venting tubes are generally equipped with an on/off valve 17 which is supposed to be operated by the tanker operator during refill procedures. Specifically, prior to filling the tank 10 through an inlet tube 18, the operator should close the venting valve 17. Failure to do this results in rapid discharge of the contained gas fumes from the tank as the incoming liquid gas drives the fumes contained in the open space 15 out the venting tube 16. When the venting valve has been properly closed, the fumes are retained in the tank and build in pressure as the tank is filled. Upon completion of fluid discharge, the operator should properly vent the pressurized fumes into the tanker for controlled disposition. Finally, the venting valve should be reopened. If the operator fails to open the venting valve, the tank may be collapsed upon withdrawal of gas through the pump 12. In view of the risk of forgetting to reopen the valve, as well as a disconcern for the effects of venting the contained fumes to the atmosphere, many operators simply ignore these proper procedures.
In an effort to meet the requirements of antipollution regulations, several devices have been developed to automatically withdraw gas fumes concurrently with the refill operation. U.S. Pat. No. 4,094,346 of Milo discloses a tank manifold which includes a liquid fill section to dispense gas into the tank, and a vapor return section to permit extraction of fumes. This vapor return section comprises a float valve which is designed to close in response to backfill of liquid gas. When in the open position, the vapor return channels the fumes back to the tanker. It is designed to remain open in response to venting fumes from the gasoline storage tank.
Other prior art which is somewhat related to vapor recovery includes U.S. Pat. Nos. 3,983,913 by Bower; 2,802,492 by Gosselin; 3,732,902 by Muller; and 3,907,010 by Burtis, et al. Each of these patents disclose method or structure for vapor recovery. In each case, however, the proposed solution to the vapor control problem involves modification of the tanker with expensive equipment to monitor fluid levels, vapor pressure and flow, or other parameters which assist in regulation of the refilling procedure. The expense and maintenance requirement of this specialized equipment presents a serious impediment to voluntary compliance with antipollution practice.